[A strategy for studying a mutation].

In this short survey, the author analyzes the main principles and some of the methods used for the analysis, at the molecular level, of a mutation causing a monogenic disease. The recent advances in molecular biology techniques allow the identification of such a molecular lesion in the human genome. A molecular probe, i.e. an isolated fragment of DNA, is the main tool for such a purpose; it is necessary for recognizing, isolating and analyzing an abnormal gene. When no molecular probe is available or when the primary defect responsible for the disease is unknown (Duchenne muscular dystrophy, cystic fibrosis), the strategy of "reverse genetics" briefly exposed here is a breakthrough in the molecular genetics of hereditary diseases.